Abstract

Ultrafast vibrational spectroscopy experiments, together with molecular-level theoretical interpretation, can provide important information about the structure and dynamics of complex condensed phase systems, including liquids. The theoretical challenge is to calculate the instantaneous vibrational frequencies of a molecule in contact with a molecular environment, accurately and quickly, and to this end a number of different methods have been developed. In this paper we critically analyze these different methods by comparing their results to accurate benchmark calculations on azide/water clusters. We also propose an optimized quantum mechanics/molecular mechanics method, which for this problem is superior to the other methods.

Received 30 December 2005Accepted 06 April 2006Published online 26 May 2006

Acknowledgments:

The authors thank Ned Sibert, Qiang Cui, and Frank Weinhold for helpful discussions. The authors are grateful for support from the National Science Foundation, through Grant Nos. CHE-0132538 and CHE-0446666, and from the Fannie and John Hertz Foundation through a fellowship to one of the authors (J.R.S.). Another author (S.A.C.) also acknowledges the support of a Ruth L. Kirschstein National Research Service Award administered through the National Institutes of Health.